docs(date-range-picker): Include docs for DateRangepicker custom format

Added the demo of custom format for date range picker
I've tried to find this many times, and probably others do to :)

demo/src/app/components/+datepicker/demos/custom-format/custom-format.html

@@ -48,4 +48,21 @@
       <button class="btn btn-success" (click)="dpFull.toggle()" [attr.aria-expanded]="dpFull.isOpen">Date Picker</button>
     </div>
   </div>
+
+  <div class="row">
+    <div class="col-xs-12 col-md-5 col-lg-4 form-group">
+      <input type="text"
+        class="form-control"
+        [minDate]="minDate"
+        [maxDate]="maxDate"
+        formControlName="myDateRange"
+        #dRP="bsDaterangepicker"
+        bsDaterangepicker
+        [bsConfig]="{ rangeInputFormat: 'MMMM Do YYYY, h:mm:ss a' }">
+    </div>
+    <div class="col-xs-12 col-12 col-md-3 form-group">
+      <button class="btn btn-success" (click)="dRP.toggle()" [attr.aria-expanded]="dRP.isOpen">Date Range Picker</button>
+    </div>
+
+  </div>
 </form>

demo/src/app/components/+datepicker/demos/custom-format/custom-format.ts

@@ -12,6 +12,7 @@ export class DemoDatePickerCustomFormatComponent {
   myForm = new FormGroup({
     myDateYMD: new FormControl(new Date()),
     myDateFull: new FormControl(new Date()),
-    myDateMDY: new FormControl(new Date())
+    myDateMDY: new FormControl(new Date()),
+    myDateRange: new FormControl([new Date(), new Date()])
   });
 }